White flame-resistant uv-stable thermoformable film made from a crystallisable thermoplastic,a method for production and the use thereof

ABSTRACT

The invention relates to a white, flame-resistant, UV-stable, thermoformable, oriented film made from a crystallisable thermoplastic, the thickness of which lies in the range of from 10 μm to 350 μm. Said film comprises at least one white pigment, a flame-proofing agent and a UV absorber and is characterized by good stretchability and thermoformability, by good optical and mechanical properties and an economical production. The invention further relates to a method for the production of said film and the use thereof.

[0001] The invention relates to a white, flame-retardant, UV-resistant,thermoformable, oriented film made from a crystallizable thermoplastic,the thickness of the film being in the range from 10 to 350 μm. The filmcomprises at least one white pigment and one flame retardant and one UVabsorber and has good orientability and thermoformability, and very goodoptical and mechanical properties, and can be produced cost-effectively.The invention further relates to the use of this film and to a processfor its production.

BACKGROUND OF THE INVENTION

[0002] White, oriented films made from crystallizable thermoplasticswith a thickness of from 10 to 350 μm are well known.

[0003] These films do not comprise UV absorbers of any kind as lightstabilizers and do not comprise flame retardants of any kind, andtherefore neither the films nor the items produced from them aresuitable for outdoor applications which demand fire protection or flameretardancy. The films do not pass the fire tests to DIN 4102 Part 2 andPart 1, or the UL 94 test. The films have inadequate thermoformability.

[0004] Even after a short time in outdoor applications, these filmsyellow and exhibit impairment of mechanical properties due tophotooxidative degradation by sunlight.

[0005] EP-A-0 620 245 describes films with improved heat resistance.These films comprise antioxidants which are suitable for scavenging freeradicals formed in the film and degrading any peroxide formed. However,that specification gives no proposal as to how the UV resistance ofthese films might be improved.

[0006] DE-A 2346 787 describes a flame-retardant polymer. Alongside thepolymer, the use of the polymer is also claimed for producing films orfibers.

[0007] The following shortcomings were apparent during production offilms from this phospholane-modified polymer:

[0008] The polymer is very susceptible to hydrolysis and has to be verythoroughly predried. The polymer cakes during its drying by prior-artdryers, and it is impossible to produce a film except under the mostdifficult of conditions.

[0009] The films produced under extreme and uneconomic conditionsembrittle on exposure to heat, i.e. the mechanical properties areseverely impaired due to substantial embrittlement, making the filmunusable. This embrittlement occurs after as little as 48 hours ofexposure to heat.

[0010] It was an object of the present invention to provide a white,flame-retardant, UV-resistant, thermoformable, oriented film with athickness of from 10-350 μm which not only can be producedcost-effectively and has good orientability and good mechanical andoptical properties, but in particular is flame retardant, does notembrittle on exposure to heat, is thermoformable, and has high UVresistance.

[0011] Flame retardancy means that in a fire test the white filmcomplies with the conditions of DIN 4102 Part 2 and in particular theconditions of DIN 4102 Part 1, and can be allocated to constructionmaterials class B 2 and in particular B1 for low-flammability materials.

[0012] The film is also intended to pass the UL 94 test “VerticalBurning Test for Flammability of Plastic Material”, permitting itsclassification in class 94 VTM-0. This means that 10 seconds afterremoval of the Bunsen burner the film has ceased to burn, and after 30seconds no glowing is observed, and no drips are found to occur.

[0013] High UV resistance means that sunlight or other UV radiationcauses no, or only extremely little, damage to the films, so that thefilms are suitable for outdoor applications and/or critical indoorapplications. In particular, after a number of years in outdoorapplications the films are intended not to yellow, nor to exhibit anyembrittlement or surface cracking, nor to exhibit any impairment ofmechanical properties. High UV resistance therefore means that the filmabsorbs UV light and does not transmit light until the visible regionhas been reached.

[0014] Thermoformability means that the film can be thermoformed to givecomplex and large-surface-area moldings on commercially availablethermoforming machinery, without uneconomic predrying.

[0015] Examples of good optical properties include uniform coloration,high surface gloss (>15), low light transmission (<70%), and also aYellowness Index unchanged from that of the flame-retardant andUV-modified film.

[0016] Good mechanical properties include high modulus of elasticity(E_(MD)>3200 N/mm²: E_(TD)>3500 N/mm²), and also good values for tensilestress at break (in MD >100 N/mm²; in TD >130 N/mm²).

[0017] Good orientability includes the capability of the film to giveexcellent orientation, both in a longitudinal direction and I transversedirection during its production, without break-offs.

[0018] Cost-effective production includes the capability of the rawmaterials or raw material components needed to produce theflame-retardant film to be dried using industrial-standard dryers. It isimportant that the raw materials neither cake nor become thermallydegraded. These prior-art industrial dryers include vacuum dryers,fluidized-bed dryers, fixed-bed dryers (tower dryers). These dryersoperate at temperatures of from 100 to 170° C., at which theflame-retardent polymers cake and have to be dug out, making filmproduction impossible.

[0019] In the case of the vacuum dryer, which provides the mildestdrying conditions, the raw material traverses a temperature range fromabout 30 to 130 ° C., under a vacuum of 50 mbar. Post-drying is thenneeded in a hopper at temperatures from 100 to 130° C. with a residencetime of from 3 to 6 hours. Here, too, this polymer cakes to an extremeextent.

BRIEF DESCRIPTION OF THE INVENTION

[0020] This object is achieved by means of a white thermoformable filmwith a thickness in the range from 10 to 350 μm, which comprises acrystallizable thermoplastic principal constituent, and comprises atleast one white pigment, at least one UV absorber, and at least oneflame retardant, where expediently the UV absorber and according toinvention the flame retardant are fed directly as masterbatch during theproduction of the film.

DETAILED DESCRIPTION OF THE INVENTION

[0021] The white, flame-retardant, UV-resistant, thermoformable,oriented film comprises, as principal constituent, a crystallizablethermoplastic. Examples of suitable crystallizable or semicrystallinethermoplastics are polyethylene terephthalate, polybutyleneterephthalate, polyethylene naphthalate, preferably polyethyleneterephthalate.

[0022] According to the invention, crystallizable thermoplastics arecrystallizable homopolymers, crystallizable copolymers, crystallizablecompounded materials (mixtures), crystallizable recycled material, andother types of crystallizable thermoplastics.

[0023] The white film may be either a single-layer or a multilayer film.The film may also have a coating of various copolyesters or adhesionpromoters.

[0024] According to the invention, the white film comprises a UVabsorber and a flame retardant. The UV absorber is expediently feddirectly during the production of the film by way of masterbatchtechnology, the concentration of the UV stabilizer preferably being from0.01 to 5% by weight, based on the weight of the layer of thecrystallizable thermoplastic.

[0025] No embrittlement on brief exposure to heat means that after 100hours of a heat-conditioning procedure at 100° C. in a circulating-airoven the film or the molding exhibits no embrittlement nor any poormechanical properties.

[0026] The film of the invention comprises at least one flame retardant,fed directly during the production of the film by way of masterbatchtechnology, the concentration of the flame retardant being in the rangefrom 0.5 to 30.0% by weight, preferably from 1.0 to 20.0% by weight,based on the weight of the layer of the crystallizable thermoplastic.The ratio of flame retardant to thermoplastic maintained duringproduction of the masterbatch is generally in the range from 60:40% byweight to 10:90% by weight.

[0027] Typical flame retardants include bromine compounds,chloroparaffins, and 10 other chlorine compounds, antimony trioxide,aluminum trihydrates, the halogen compounds being disadvantageous due tothe halogen-containing by-products produced. Another extremedisadvantage is the low lighffastness of a film modified therewith,alongside the evolution of hydrogen halides in the event of a fire.

[0028] Examples of suitable flame retardants used according to theinvention are organophosphorus compounds, such as carboxyphosphinicacids, anhydrides of these, and dimethyl methylphosphonate. It isimportant for the invention that the organophosphorus compound issoluble in the thermoplastic, since otherwise the optical propertiesrequired are not complied with.

[0029] Since the flame retardants generally have some susceptibility tohydrolysis, it can be advisable to add a hydrolysis stabilizer.

[0030] Hydrolysis stabilizers used are generally phenolic stabilizers,alkali metal/alkaline earth metal stearates, and/or alkalimetal/alkaline earth metal carbonates, in amounts of from 0.01 to 1.0%by weight. It is preferable to use amounts of from 0.05 to 0.6% byweight, in particular from 0.15 to 0.3% by weight, of phenolicstabilizers having a molar mass above 500 g/mol. Particularlyadvantageous compounds are pentaerythrityltetrakis-3-(3,5-di-tert-butyl-4-hydroxphenyl) propionate or1,3,5-trimethyl-2,4,6-tris(3,5-di-tert-butyl-4-hydroxybenzyl)benzene.

[0031] The white pigment is preferably fed by way of masterbatchtechnology, but may also be incorporated directly at the premises of thepolymer producer. The concentration of the white pigment is from 0.2 to40% by weight, preferably from 0.5 to 25% by weight, based on the weightof the crystallizable thermoplastic.

[0032] Preferred suitable white pigments are titanium dioxide, bariumsulfate, calcium carbonate, kaolin, silicon dioxide, preferably titaniumdioxide and barium sulfate.

[0033] The titanium dioxide particles may be composed of anatase orrutile, preferably predominantly of rutile, which has higher opacifyingpower than anatase.

[0034] In a preferred embodiment, the titanium dioxide particles arecomposed of at least 95% by weight of rutile. They may be prepared by aconventional process, e.g.: by the chloride process or the sulfateprocess. The amount of these in the base layer is from 0.3 to 25% byweight, based on the base layer, and the average particle size isrelatively small, preferably in the range from 0.10 to 0.30 μm.

[0035] Titanium dioxide of the type described does not produce anyvacuols within the polymer matrix during the production of the film.

[0036] The titanium dioxide particles may have the type of coveringusually used as a covering for TiO₂ white pigment in papers or paints toimprove lightfastness, made from inorganic oxides.

[0037] TiO₂ is known to be photoactive. On exposure to UV radiation,free radicals form on the surface of the particles. These free radicalscan migrate into the film-forming polymers, causing degradationreactions and yellowing.

[0038] Particularly suitable oxides include the oxides of aluminum,silicon, zinc, or magnesium, and mixtures made from two or more of thesecompounds. TiO₂ particles with a covering made from two or more of thesecompounds are described by way of example in EP-A-0 044 515 and EP-A-0078 633. The coating may also comprise organic compounds having polarand non-polar groups. The organic compounds have to have adequatethermal stability during production of the film by extrusion of thepolymer melt. Examples of polar groups are —OH, —OR, —COOX (X═R, H, orNa, R=alkyl having from 1 to 34 carbon atoms). Preferred organiccompounds are alkanols and fatty acids having from 8 to 30 carbon atomsin the alkyl group, in particular fatty acids and primary n-alkanolshaving from 12 to 24 carbon atoms, and also polydiorganosiloxanes and/orpolyorganohydrosiloxanes, e.g. polydimethylsiloxane andpolymethylhydrosiloxane.

[0039] The coating for the titanium dioxide particles is usuallycomposed of from 1 to 12 g, in particular from 2 to 6 g, of inorganicoxides, and from 0.5 to 3 g, in particular from 0.7 to 1.5 g, of organiccompounds, based on 100 g of titanium dioxide particles. The covering isapplied to the particles in aqueous suspension. The inorganic oxides maybe precipitated from water-soluble compounds, e.g. alkali metal nitrate,in particular sodium nitrate, sodium silicate (waterglass), or silica,in the aqueous suspension.

[0040] For the purposes of the present invention, inorganic oxides, suchas Al₂O₃ or SiO₂, also include the hydroxides and their various stagesof dehydration, e.g. oxide hydrate, the precise composition andstructure of which is not known. The oxide hydrates, e.g. of aluminumand/or of silicon, are precipitated onto the calcined and ground TiO₂pigment, in aqueous suspension, and the pigments are then washed anddried. This precipitation may therefore take place directly in asuspension such as that produced within the production process aftercalcination followed by wet-grinding. The oxides and/or oxide hydratesof the respective metals are precipitated from the water-soluble metalsalts within the known pH range: for example, for aluminum use is madeof aluminum sulfate in aqueous solution (pH below 4), and the oxidehydrate is precipitated within the pH range from 5 to 9, preferably from7 to 8.5, by addition of aqueous ammonia solution or sodium hydroxidesolution. If the starting material is waterglass solution or alkalimetal aluminate solution, the pH of the initial charge of TiO₂suspension should be within the strongly alkaline range (pH above 8).The precipitation then takes place within the pH range from 5 to 8, byaddition of mineral acid, such as sulfuric acid. Once the metal oxideshave been precipitated, the stirring of the suspension continues forfrom 15 min to about 2 h, aging the precipitated layers. The coatedproduct is separated off from the aqueous dispersion, washed, and driedat an elevated temperature, in particular at from 70 to 100° C.

[0041] Light, in particular the ultraviolet content of solar radiation,i.e. the wavelength region from 280 to 400 nm, induces degradation inthermoplastics, as a result of which their appearance changes due tocolor change or yellowing, and there is also an adverse effect onmechanical/physical properties.

[0042] Inhibition of this photooxidative degradation is of considerableindustrial and economic importance, since otherwise there are drasticlimitations on the applications of many thermoplastics.

[0043] Absorption of UV light by polyethylene terephthalates, forexample, starts at below 360 nm, increases markedly below 320 nm, and isvery pronounced at below 300 nm. Maximum absorption occurs at from 280to 300 nm.

[0044] In the presence of oxygen it is mainly chain cleavage whichoccurs, without any crosslinking. The predominant photooxidationproducts in quantity terms are carbon monoxide, carbon dioxide, andcarboxylic acids. Besides the direct photolysis of the ester groups,consideration has to be given to oxidation reactions which likewise formcarbon dioxide, via peroxide radicals.

[0045] In the photooxidation of polyethylene terephthalates there canalso be cleavage of hydrogen at the position α to the ester groups,giving hydroperoxides and decomposition products of these, and this maybe accompanied by chain cleavage (H. Day, D. M. Wiles: J. Appl. Polym.Sci 16, 1972, p. 203).

[0046] UV stabilizers, i.e. light stabilizers which are UV absorbers,are chemical compounds which can intervene in the physical and chemicalprocesses of light-induced degradation. Carbon black and other pigmentscan give some protection from light. However, these substances areunsuitable for transparent films, since they cause discoloration orcolor change. The only compounds suitable for transparent matt films areorganic and organometallic compounds which produce no, or only extremelyslight, color or color change in the thermoplastic to be stabilized,i.e. those which are soluble in the thermoplastic.

[0047] For the purposes of the present invention, UV stabilizerssuitable as light stabilizers are those which absorb at least 70%,preferably 80%, particularly preferably 90%, of the UV light in thewavelength region from 180 to 380 nm, preferably 280 to 350 nm. Theseare particularly suitable if they are thermally stable in thetemperature range from 260 to 300° C., i.e. neither decompose nor giverise to release of gases. Examples of UV stabilizers suitable as lightstabilizers are 2-hydroxybenzophenones, 2-hydroxybenzotriazoles,organonickel compounds, salicylic esters, cinnamic ester derivatives,resorcinol monobenzoates, oxanilides, hydroxybenzoic esters, andsterically hindered amines and triazines, preference being given to the2-hydroxybenzotriazoles and the triazines.

[0048] The UV stabilizer(s) are preferably present in the outerlayer(s). The core layer may also have UV stabilizer, if required.

[0049] It was highly surprising that the use of the abovementioned UVstabilizers in films gave the desired result. The skilled worker wouldprobably first have attempted to achieve a certain degree of UVresistance by way of an antioxidant, but would have found that the filmrapidly yellows on weathering.

[0050] In the knowledge that UV stabilizers absorb UV light andtherefore provide protection, the skilled worker would be likely to haveused commercially available stabilizers. He would then have observedthat

[0051] the UV stabilizer has unsatisfactory thermal stability, and attemperatures of from 200 to 240° C. decomposes and gives rise to releaseof gases, and

[0052] large amounts (from about 10 to 15% by weight) of the UVstabilizer have to be incorporated in order to absorb the UV light andthus prevent damage to the film.

[0053] At these high concentrations it would have been observed that thefilm is yellow even just after it has been produced, with YellownessIndices (YI) of around 25. It would also have been observed that themechanical properties of the film have been adversely affected.Orientation would have produced exceptional problems, such as

[0054] break-offs due to unsatisfactory strength, i.e. excessively lowmodulus of elasticity;

[0055] die deposits, causing profile variations;

[0056] roller deposits from the UV stabilizer, causing impairment ofoptical properties (defective adhesion, non-uniform surface);

[0057] deposits in stretching frames or heat-setting frames, droppingonto the film.

[0058] It was therefore more than surprising that even lowconcentrations of the UV stabilizer achieve excellent UV protection. Itwas very surprising that, together with this excellent UV protection,

[0059] within the accuracy of measurement, the Yellowness Index of thefilm is unchanged from that of an unstabilized film;

[0060] there are no releases of gases, no die deposits, and no framecondensation, and the film therefore has excellent optical propertiesand excellent profile and layflat, and

[0061] the UV-resistant film has excellent stretchability, and cantherefore be produced in a reliable and stable manner on high-speed filmlines at speeds of up to 420 m/min.

[0062] It was more than surprising that the use of masterbatchtechnology and of appropriate predrying and/or precrystallization and,where appropriate, use of small amounts of a hydrolysis stabilizerpermit the production of a flame-retardant and thermoformable film withthe property profile demanded in a cost-effective manner and withoutcaking in the dryer, and that the film does not embrittle on exposure toheat and does not fracture when creased. It was very surprising thattogether with this excellent result and the required flame retardancy,and the thermoformability and high UV resistance

[0063] within the accuracy of measurement, the Yellowness Index of thefilm is not adversely affected when compared with that of anunstabilized film;

[0064] there are no releases of gases, no die deposits, and no framecondensation, and the film therefore has excellent optical propertiesand excellent profile and layflat, and

[0065] the flame-retardant UV-resistant film has excellentstretchability, and can therefore be produced in a reliable and stablemanner on high-speed film lines at speeds of up to 420 m/min.

[0066] With this, the film is also cost-effective.

[0067] It was also surprising that a higher diethylene glycol contentand/or polyethylene glycol content and/or IPA content than that ofstandard thermoplastics permits cost-effective thermoforming of thefilms on commercially available thermoforming plants, and gives thefilms capability for excellent reproduction of detail.

[0068] It is moreover very surprising that it is also possible to reusethe regrind produced from the films or from the moldings withoutadversely affecting the Yellowness Index of the film.

[0069] In one preferred embodiment, the white, flame-retardant film ofthe invention comprises, as principal constituent, a crystallizablepolyethylene terephthalate having a diethylene glycol content of ≧1.0%by weight, preferably ≧1.2% by weight, in particular ≧1.3% by weight,and/or a polyethylene glycol content (PEG content) of ≧1.0% by weight,preferably ≧1.2% by weight, in particular ≧1.3% by weight, from 1 to 20%by weight of an organic phosphorus compound (dimethyl methylphosphonate)as flame retardant soluble in the polyethylene terephthalate, from 0.01to 5.0% by weight of a UV absorber selected from the group of the2-hydroxybenzotriazoles or the triazines and soluble in the PET, andfrom 0.5 to 25% by weight of titanium dioxide whose preferred particlediameter is from 0.10 to 0.50 μm, preferably a rutile-type titaniumdioxide. Instead of titanium dioxide, it is also possible to use bariumsulfate whose particle diameter is from 0.20 to 1.20 μm as whitepigment, the concentration being from 1.0 to 25% by weight. In onepreferred embodiment, it is also possible to use a mixture of thesewhite pigments, or a mixture of one of these white pigments with anotherwhite pigment.

[0070] In one particularly preferred embodiment, the film of theinvention comprises from 0.01 to 5.0% by weight of2-(4,6-diphenyl-1,3,5-triazin-2-yl)-5-(hexyl) oxyphenol of the formula

[0071] or from 0.01 to 5.0% by weight of2,2′-methylenebis(6-(2H-benzotriazol-2-yl)-4-(1,1,3,3-tetramethyl-butyl)phenolof the formula

[0072] In one preferred embodiment, it is also possible to use a mixtureof these two UV stabilizers, or a mixture of at least one of these twoUV stabilizers with other UV stabilizers, the total concentration oflight stabilizer preferably being from 0.01 to 5.0% by weight, based onthe weight of crystallizable polyethylene terephthalate.

[0073] In the invention it is important for thermoformability that thecrystallizable thermoplastic has a diethylene glycol content (DEGcontent) of ≧1.0% by weight, preferably ≧1.2% by weight, in particular≧1.3% by weight, and/or a polyethylene glycol content (PEG content) of≧1.0% by weight, preferably ≧1.2% by weight, in particular ≧1.3% byweight, and/or an isophthalic acid content (IPA) of from 3 to 10% byweight.

[0074] The white, UV-resistant, thermoformable, flame-retardant film hasthe following property profile:

[0075] surface gloss, measured to DIN 67530 (measurement angle 20°), isgreater than 15, preferably greater than 20, and light transmittance L,measured to ASTM D 1003, is less than 70%, preferably less than 60%,measured to ASTM S 1003, this being surprisingly good for the UVresistance achieved in combination with the flame retardancy.

[0076] Standard viscosity SV (DCA) of the polyethylene terephthalate,measured in dichloroacetic acid to DIN 53728 is from 600 to 1000,preferably from 700 to 900.

[0077] The white polyethylene terephthalate film which comprises atleast one organic white pigment, one UV stabilizer, and one flameretardant may be either a single-layer film or a multilayer film.

[0078] In the multilayer embodiment, the film is built up from at leastone corner layer and from at least one outer layer, preference beinggiven in particular to a three-layer A-B-A or A-B-C structure.

[0079] For this embodiment it is important that standard viscosity andDEG content and/or PEG content of the polyethylene terephthalate of thecore layer are similarto those of the polyethylene terephthalate of theouter layer(s) adjacent to the core layer.

[0080] In a particular embodiment, the outer layers may also be composedof a polyethylene naphthalate homopolymer or of a polyethyleneterephthalate-polyethylene naphthalate copolymer, or of a compoundedmaterial.

[0081] Again in this embodiment, standard viscosity and DEG contentand/or PEG content of the thermoplastics of the outer layers are similarto those of the polyethylene terephthalate of the core layer.

[0082] In the multilayer embodiment, the UV absorber is preferablypresent in the outer layers. If required, UV absorber may also have beenprovided in the core layer.

[0083] In the multilayer embodiment, the white pigment and the flameretardant are preferably present in the core layer. However, ifrequired, white pigment and/or flame retardant may also have beenprovided in the outer layers.

[0084] In another embodiment it is also possible for white pigment,flame retardant and UV absorber to be present in the outer layers. Ifrequired and if fire protection requirements are stringent, the corelayer may also have what is known as a “base level” of flame retardant.

[0085] Unlike in the single-layer embodiment, the concentration of thewhite pigment here, and of the flame retardant and of the UV stabilizer,is based on the weight in the modified layer. Highly surprisingly,weathering tests to the ISO 4892 test specification using the Atlas C165Weather Ometer have shown that in order to achieve improved UVresistance for a three-layer film it is fully sufficient for the outerlayers of thickness of from 0.5 to 2 μm to be provided with UVstabilizers. Fire tests to DIN 4102 Part 1 and Part 2, and also the UL94 test have equally surprisingly shown that compliance of the film ofthe invention with the requirements extends to the range of thicknessfrom 5 to 300 μm.

[0086] The flame-retardant, UV-resistant, thermoformable, multilayerfilms produced using known coextrusion technology are therefore of greateconomic interest when compared with monofilms provided with UVstabilizers and flame retardants throughout, since markedly lessadditives are needed for comparable flame retardancy and UV resistance.

[0087] At least one side of the film may also have been provided with ascratch-resistant coating, with a copolyester, or with an adhesionpromoter.

[0088] Weathering tests have shown that even after from 5 to 7 years ofoutdoor use (extrapolated from the weathering tests) the flame-retardantUV-resistant films of the invention generally exhibit no increasedyellowing, no embrittlement, no loss of surface gloss, no surfacecracking, and no impairment of mechanical properties.

[0089] The results of measurements indicate that the film of theinvention or the molding does not embrittle when exposed to heat at 100°C. over a prolonged period. This result is attributable to thesynergistic action of appropriate precrystallization, predrying,masterbatch technology, and modification with UV stabilizer.

[0090] The film can be thermoformed without predrying, and can thereforebe used to produce complex moldings.

[0091] The thermoforming process generally encompasses the steps ofpredrying, heating, molding, cooling, demolding, and heat-conditioning.Surprisingly, during the thermoforming process it was found that thefilms of the invention can be thermoformed without prior predrying. Thisadvantage over thermoformable polycarbonate films or thermoformablepolymethacrylate films, which require predrying times of from 10 to 15hours, at temperatures of from 100 to 120° C., depending on thickness,drastically reduces the costs of the forming process.

[0092] The following process parameters for the thermoforming processwere found: Step of process Film of invention Predrying not requiredTemperature of mold ° C. from 100 to 160 Heating time <5 sec per 10 μmof film thickness Film temperature during from 160 to 220 thermoforming° C. Possible orientation factor from 1.5 to 2.0 Reproduction of detailgood Shrinkage (%) <1.5

[0093] The film of the invention or the molding produced therefrom canmoreover be recycled without difficulty and without pollution of theenvironment, and without loss of mechanical properties, and is thereforesuitable for use as short-lived advertising placards, for example, forthe construction of exhibition stands, or for other promotional itemswhere fire protection and thermoformability is desired.

[0094] An example of a method for producing the white, flame-retardant,thermoformable, UV-resistant film of the invention is the extrusionprocess on an extrusion line.

[0095] According to the invention, the flame retardant is added by wayof masterbatch technology. The flame retardant is fully dispersed in acarrier material. Carrier materials which may be used are thethermoplastic itself, e.g. the polyethylene terephthalate, or else otherpolymers compatible with the thermoplastic.

[0096] According to the invention, the UV stabilizer and the whitepigment may be fed before the material leaves the producer of thethermoplastic polymer, or during the production of the film, into theextruder.

[0097] DEG content and/or PEG content of the polyethylene terephthalateare set at the premises of the polymer producer during thepolycondensation process.

[0098] Addition of the white pigment and of the UV stabilizer by way ofmasterbatch technology is particularly preferred. The UV stabilizer and,respectively, the white pigment is fully dispersed in a solid carriermaterial. Carrier materials which may be used are the thermoplasticitself, e.g. the polyethylene terephthalate, or else other polymerssufficiently compatible with the thermoplastic.

[0099] It is important in masterbatch technology that the grain size andthe bulk density of the masterbatch are similar to the grain size andthe bulk density of the thermoplastic, thus permitting uniformdistribution and, with this, uniform UV resistance.

[0100] The polyester films may be produced by known processes from apolyester, where appropriate with other polymers, with the flameretardant, with the white pigment, with the UV absorber, and/or withother conventional additives in conventional amounts from 1.0 to notmore than 30% by weight, either in the form of a monofilm or else in theform of multilayer, where appropriate coextruded films with surfaces ofidentical or different nature, for example pigment being present in onesurface but no pigment being present in the other surface. It is alsopossible for one or both surfaces of the film to be provided with aconventional functional coating by known processes.

[0101] It is important for the invention that the masterbatch whichcomprises the flame retardant and, where appropriate, the hydrolysisstabilizer, is precrystallized or predried. This predrying includesprogressive heating of the masterbatch at subatmospheric pressure (from20 to 80 mbar, preferablyfrom 30 to 60 mbar, in particular from 40 to 50mbar), with stirring, and, where appropriate, post-drying at a constantelevated temperature, again at subatmospheric pressure. The masterbatchis preferably charged at room temperature from a feed vessel in thedesired blend with the polymers of the base and/or outer layers and,where appropriate, with other raw material components, batchwise in avacuum dryer which during the course of the drying time or residencetime traverses a temperature profile from 10 to 160° C., preferably from20 to 150° C., in particular from 30 to 130° C. During the residencetime of about 6 hours, preferably 5 hours, in particular 4 hours, theraw material mixture is stirred at from 10 to 70 rpm, preferably from 15to 65 rpm, in particular from 20 to 60 rpm. The resultantprecrystallized or predried raw material mixture is post-dried for from2 to 8 hours, preferably from 3 to 7 hours, in particular from 4 to 6hours, in a downstream vessel, likewise evacuated, at from 90 to 180°C., preferably from 100 to 170° C., in particular from 110 to 160° C.

[0102] In the preferred extrusion process for producing the polyesterfilm, the molten polyester material is extruded through a slot die and,in the form of a substantially amorphous prefilm, quenched on a chillroll. This film is then reheated and stretched longitudinally andtransversely, or transversely and longitudinally, or longitudinally,transversely, and again and longitudinally and/or transversely. Thestretching temperatures are generally from T_(G)+10° C. to T_(G)+60° C.(T_(G)=glass transition temperature), and the stretching ratio forlongitudinal stretching is usually from 2 to 6, in particular from 3 to4.5, and that for transverse stretching is from 2 to 5, in particularfrom 3 to 4.5, and that for any second longitudinal or transversestretching carried out is from 1.1 to 5. The first longitudinalstretching may, where appropriate, take place simultaneously withtransverse stretching (simultaneous stretching). Heat-setting of thefilm then follows with oven temperatures of from 180 to 260° C., inparticular from 220 to 250° C. The film is then cooled and wound.

[0103] The surprising combination of exceptional properties gives thefilm of the invention excellent suitability for a wide variety ofapplications, for example for interior decoration, for exhibition standsor exhibition requisites, as displays, for placards, for protectiveglazing of machinery or of vehicles, in the lighting sector, in thefitting-out of shops or of stores, as a promotional item or laminatingmedium, for greenhouses, for roofing systems, external cladding,protective coverings, applications in the construction sector, andilluminated advertising profiles, blinds, or electrical applications.

[0104] Its thermoformability makes the film of the invention suitablefor thermoforming desired moldings for indoor or outdoor applications.

[0105] The invention is further illustrated below using examples.

[0106] The following standards or methods are used here in measuring theindividual properties.

TEST METHODS

[0107] DEG Content, PEG Content and IPA Content

[0108] DEG, PEG, or IPA content is determined by gas chromatographyafter dissolving the thermoplastic polymer in cresol.

[0109] Surface Gloss

[0110] Surface gloss is measured at a measurement angle of 20° to DIN67530.

[0111] Light Transmittance

[0112] Light transmittance is the ratio of the total transmitted lightto the amount of incident light. Light transmittance is measured usingthe “®HAZEGARD plus” tester to ASTM D 1003.

[0113] Haze

[0114] Haze is that percentage proportion of transmitted light whichdeviates by more than 2.50 from the average direction of the incidentlight beam. Clarity is determined at an angle of less than 2.50.

[0115] Haze is [lacuna] using the “HAZEGARD plus” tester to ASTM D 1003.

[0116] Surface Defects

[0117] Surface defects are determined visually.

[0118] Mechanical Properties

[0119] Modulus of elasticity and tensile stress at break, and tensilestrain at break, are measured longitudinally and transversely to ISO527-1-2.

[0120] SV (DCA), IV (DVA)

[0121] Standard viscosity SV (DCA) is measured by a method based on DIN53726 in dichloroacetic acid.

[0122] Intrinsic viscosity (IV) is calculated from standard viscosity asfollows

IV (DCA)=6.67·10⁻⁴SV(DCA)+0.118

[0123] Fire Performance

[0124] Fire performance is determined to DIN 4102 Part 2, constructionmaterials class B2, and to DIN 4102 Part 1, construction materials classB1, and also to the UL 94 test.

[0125] Weathering (Bilateral), UV Resistance

[0126] UV resistance is tested as follows to the ISO 4892 testspecification: Tester Atlas Ci 65 Weather Ometer Test conditions Iso4892, i.e. artificial weathering Irradiation time 1 000 hours (per side)Irradiation 0.5 W/m², 340 nm Temperature 63° C. Relative humidity 50%Xenon lamp internal and external filter made from borosilicateIrradiation cycles 102 minutes of UV light, then 18 minutes of UV lightwith water spray on the specimens, then again 102 minutes of UV light,etc.

[0127] Yellowness Index

[0128] (YI) is the deviation from the colorless condition in the“yellow” direction and is measured to DIN 6167. Yellowness indices (YIs)<5 are not visually detectable.

[0129] In each case, the examples and comparative examples below usewhite films of varying thickness, produced on the extrusion linedescribed.

[0130] All of the films were weathered bilaterally to ISO 4892 testspecification, in each case for 1000 hours per side using the Atlas Ci65 Weather Ometer from the company Atlas, and then tested for mechanicalproperties, Yellowness Index (YI), surface defects, light transmission,and gloss.

[0131] Fire tests to DIN 4102, Part 2 and Part 1, and the UL 94 test,were carried out on all of the films.

EXAMPLES Example 1

[0132] A white film of 50 m thickness is produced and comprises, asprincipal constituent, polyethylene terephthalate, 7.0% by weight oftitanium dioxide, and 1.0% by weight of the UV stabilizer2-(4,6-diphenyl-1,3,5-triazin-2-yl)-5-(hexyl)oxyphenol (®Tinuvin 1577from the company Ciba-Geigy) and 2.0% by weight of flame retardant.

[0133] The titanium dioxide is of rutile type and has an averageparticle diameter of 0.20 μm, and has a coating of Al₂O₃. ®Tinuvin 1577has a melting point of 149° C. and is thermally stable up to about 330°C.

[0134] For purposes of uniform distribution, the titanium dioxide andthe UV absorber is incorporated into the PET directly at the premises ofthe polymer producer.

[0135] The flame retardant is the PET soluble organophosphorus compoundAmgard P1045 from the company Albright & Wilson.

[0136] The flame retardant is fed in the form of a masterbatch. Themasterbatch is composed of 10% by weight of flame retardant and 80% byweight of PET, and its bulk density is 750 kg/m³.

[0137] The PET from which the film is produced and the PET that isutilized for masterbatch production have standard viscosity SV (DCA) of810, corresponding to intrinsic viscosity IV (DCA) of 0.658 dl/g. DEGcontent and PEG content are 1.6% by weight. 50% of the polyethyleneterephthalate, 30% by weight of recycled polyethylene terephthalatematerial, and 20% by weight of the masterbatch are charged at roomtemperature from separate feed vessels in a vacuum dryer which from thejuncture of charging to the end of the residence time traverses atemperature profile from 25 to 130° C. During the residence time ofabout 4 hours, the raw material mixture is stirred at 61 rpm.

[0138] The precrystallized or predried raw material mixture ispost-dried in the downstream hopper, likewise under vacuum, at 140° C.for 4 hours. The 50 μm monofilm is then produced using the extrusionprocess described.

[0139] The individual steps of the process were: LongitudinalTemperature: 85-135° C. stretching Longitudinal stretching ratio: 4.0:1Transverse Temperature: 85-135° C. stretching Transverse stretchingratio: 4.0:1 Setting Temperature: 230° C.

[0140] The white PET film produced had the following property profile:Thickness 50 μm Surface gloss side 1 72 (Measurement angle 20°) side 268 Light transmittance 28% Surface defects per m² none Longitudinalmodulus of elasticity 3 700 N/mm² Transverse modulus of elasticity 4 800N/mm² Longitudinal tensile stress at break 130 N/mm² Transverse tensilestress at break 205 N/mm² Yellowness Index (YI) 48 Coloration uniform

[0141] The film fulfills the requirements of construction materialsclasses B2 and B1 to DIN 4102 Part 2 and Part 1. The film passes the UL94 test.

[0142] After 200 hours of heat-conditioning at 100 ° C. in acirculating-air drying cabinet the mechanical properties are unaltered.The film exhibits no embrittlement phenomena of any kind.

[0143] After in each case 1000 hours of weathering per side with theAtlas CI 65

[0144] Weather Ometer the PET film has the following properties:Thickness 50 μm Surface gloss side 1 65 (Measurement angle 20°) side 260 Light transmittance 35% Surface defects per m² none Longitudinalmodulus of elasticity 3 550 N/mm² Transverse modulus of elasticity 4 650N/mm² Longitudinal tensile stress at break 118 N/mm² Transverse tensilestress at break 190 N/mm² Yellowness Index (YI) 49

Example 2

[0145] Coextrusion technology is used to produce a multilayer PET filmof thickness 17 μm with the layer sequence A-B-A, B being the core layerand A being the outer layers. The thickness of the core layer is 15 μmand that of each of the two outer layers which cover the core layer is 1μm.

[0146] The polyethylene terephthalate used for the core layer B isidentical with that of example 1 except that it comprises no UVabsorber.

[0147] The core layer moreover comprises 2% by weight of flameretardant, the flame retardant being fed in the form of a masterbatch.The masterbatch is composed of 10% by weight of flame retardant and 90%by weight of PET.

[0148] The PET of the outer layers has a standard viscosity SV (DCA) of810 and has been provided with 1% by weight of Tinuvin 1577 and 0.3% byweight of Sylobloc. The outer layers comprise no titanium dioxide and noflame retardant.

[0149] For the core layer, 50% by weight of polyethylene terephthalate,30% by weight of recycled polyethylene terephthalate material, and 20%by weight of the masterbatch are precrystallized, predried, andpost-dried as in example 1.

[0150] The outer layer polymer does not undergo any particular drying.Coextrusion technology is used to produce a film of thickness 17 μm withthe layer sequence A-B-A and with the following properties: Layerstructure A-B-A Total thickness 17 μm Surface gloss side 1 131(Measurement angle 20°) side 2 126 Light transmittance 49% Surfacedefects none (specks, orange peel, bubbles, . . . ) Longitudinal modulusof elasticity 3 550 N/mm² Transverse modulus of elasticity 4 130 N/mm²Longitudinal tensile stress at break 120 N/mm² Transverse tensile stressat break 155 N/mm² Yellowness Index (YI) 13.3 Coloration uniform

[0151] After 200 hours of heat-conditioning at 100° C. in acirculating-air drying cabinet the mechanical properties are unaltered.The film exhibits no embrittlement phenomena of any kind.

[0152] The film fulfills the requirements of construction materialsclass B2 and B1 to DIN 4102 Part 2 and Part 1. The film passes the UL 94test.

[0153] After in each case 1000 hours of weathering per side with theAtlas CI 65 Weather Ometer the PET film has the following properties:Layer structure A-B-A Total thickness 17 μm Surface gloss side 1 125(Measurement angle 20°) side 2 116 Light transmittance 45% Surfacedefects none (specks, orange peel, bubbles, . . . ) Longitudinal modulusof elasticity 3 460 N/mm² Transverse modulus of elasticity 4 050 N/mm²Longitudinal tensile stress at break 110 N/mm² Transverse tensile stressat break 145 N/mm² Yellowness Index (YI) 15.1 Coloration uniform

Example 3

[0154] A 20 μm A-B-A film is produced as in example 2, the thickness ofthe core layer B being 16 μm and that of each of the outer layers Abeing 2 μm.

[0155] The core layer B comprises only 5% by weight of the flameretardant masterbatch of example 2.

[0156] The outer layers are identical with those of example 2, exceptthat they comprise 20% by weight of the flame retardant masterbatch usedin example 2 only for the core layer.

[0157] The raw materials and the masterbatch for the core layer and theouter layers are precrystallized, predried, and postdried as in example1.

[0158] The multilayer 20 μm film produced by means of coextrusiontechnology has the following property profile: Layer structure A-B-ATotal thickness 20 μm Surface gloss side 1 136 (Measurement angle 20°)side 2 128 Light transmittance 41% Surface defects none (specks, orangepeel, bubbles, . . . ) Longitudinal modulus of elasticity 3 400 N/mm²Transverse modulus of elasticity 4 100 N/mm² Longitudinal tensile stressat break 120 N/mm² Transverse tensile stress at break 160 N/mm²Yellowness Index (YI) 13.1

[0159] After 200 hours of heat-conditioning at 100° C. in acirculating-air drying cabinet the mechanical properties are unaltered.The film exhibits no embrittlement phenomena of any kind.

[0160] The film fulfills the requirements of construction materialsclasses B2 and B1 to DIN 4102 Part 2 and Part 1. The film passes the UL94 test.

[0161] After in each case 1000 hours of weathering per side with theAtlas CI 65 Weather Ometer the PET film has the following properties:Layer structure A-B-A Total thickness 20 μm Surface gloss side 1 124(Measurement angle 20°) side 2 117 Light transmittance 38% Surfacedefects none (specks, orange peel, bubbles, . . . ) Longitudinal modulusof elasticity 3 350 N/mm² Transverse modulus of elasticity 4 000 N/mm²Longitudinal tensile stress at break 105 N/mm² Transverse tensile stressat break 140 N/mm² Yellowness Index (YI) 15.8

[0162] Thermoformability

[0163] The films of examples 1 to 3 can be thermoformed on commerciallyavailable thermoforming machinery, e.g. from the company Illig, to givemoldings, without predrying. The reproduction of detail in the moldingsis excellent, with uniform surface.

Comparative example 1

[0164] Example 2 is repeated. However, the film is not provided with UVabsorbers, nor with flame retardant masterbatch. DEG content is thecommercially available 0.7%, and no PEG is present.

[0165] The white film produced has the following property profile: Layerstructure A-B-A Total thickness 17 μm Surface gloss side 1 139(Measurement angle 20°) side 2 130 Light transmittance 50% Surfacedefects none (specks, orange peel, bubbles, . . . ) Longitudinal modulusof elasticity 4 250 N/mm² Transverse modulus of elasticity 4 700 N/mm²Longitudinal tensile stress at break 180 N/mm² Transverse tensile stressat break 215 N/mm² Yellowness Index (YI) 12.0 Coloration uniform

[0166] The unmodified film does not fulfill the requirements of thetests to DIN 4102 Part 1 and Part 2, or of the UL 94 test.

[0167] The film has inadequate thermoformability.

[0168] After 1000 hours of weathering per side using the Atlas CIWeather Ometer the film exhibits embrittlement phenomena and cracking onthe surfaces. This makes it impossible to measure the property profileprecisely—in particular the mechanical properties. Furthermore, the filmhas visible yellow coloration.

1. A white, thermoformable film with a thickness in the range from 1 to350 μm, which comprises a crystallizable thermoplastic principalconstituent, and comprises at least one white pigment, at least one UVstabilizer, and at least one flame retardant which flame retardant issoluble in the thermoplastic and is fed directly during the productionof the film by way of masterbatch technology, wherein the masterbatchhas been pretreated by gradual heating at subatmospheric pressure, withstirring.
 2. The film as claimed in claim 1, wherein the gradual heatingat subatmospheric pressure, with stirring, is directly followed bypost-drying at a constant, elevated temperature, again at subatmosphericpressure.
 3. The film as claimed in claim 1, wherein the concentrationof the UV stabilizer is in the range from 0.01 to 5% by weight, based onthe weight of the crystallizable thermoplastic.
 4. The film as claimedin claim 1, wherein the UV stabilizer is selected from one or more of2-hydroxy-benzotriazols and triazines.
 5. The film as claimed in claim4, wherein the UV stabilizer is selected from one or more of2-(4,6-diphenyl-1,3,5-triazin-2-yl)-5-(hexyl) oxyphenol and2,2′-methylenebis(6-(2H-benzotriazol-2-yl)-4-(1,1,3,3-tetramethy-butl)phenol.6. The film as claimed in claim 1, wherein the flame retardant isselected from one or more organophosphorus compounds.
 7. The film asclaimed in claim 6, wherein the flame retardant is dimethylmethylphosphonate.
 8. The film as claimed in claim 1, which comprisesfrom 0.5 to 30.0% by weight of flame retardants.
 9. The film as claimedin claim 1, wherein the white pigment is selected from one or more ofthe white pigments titanium dioxide, barium sulfate, calcium carbonate,kaolin, and silicon dioxide.
 10. The film as claimed in claim 9, whereinthe white pigment is titanium dioxide.
 11. The film as claimed in claim1, wherein the white pigment has a coating.
 12. The film as claimed inclaim 1, wherein the amount of white pigment is from 0.2-40% by weight,based on the weight of the polymer layer in which the white pigment ispresent.
 13. The film as claimed in claim 1, wherein the averageparticle size of the white pigment is from 0.10-0.30 μm.
 14. The film asclaimed in claim 1, wherein the surface gloss measured to DIN 67530(measurement angle 20°) is greater than
 15. 15. The film as claimed inclaim 1, wherein the light transmittance measured to ASTM D 1003 issmaller than 70%.
 16. The film as claimed in claim 1, wherein themodulus of elasticity measured to ISO 527-1-2 is greater than 3200 N/mm²longitudinally and greater than 3500 N/mm² transversely.
 17. The film asclaimed in claim 1, wherein the crystallizable thermoplastic is selectedfrom polyethylene terephthalate, polybutylene terephthalate,polyethylene naphthalate, and mixtures of one or more of thesethermoplastics.
 18. The film as claimed in claim 17, whereinpolyethylene terephthalate is used as crystallizable thermoplastic. 19.The film as claimed in claim 18, which comprises recycled material. 20.The film as claimed in claim 1, which has a single-layer structure. 21.The film as claimed in claim 1, which has a multilayer structure with atleast one outer layer and with at least one core layer.
 22. The film asclaimed in claim 21, wherein the multilayer structure has two outerlayers and a core layer located between the outer layers.
 23. The filmas claimed in claim 21 or 22, wherein at least one UV stabilizer ispresent in the outer layer or layers.
 24. The film as claimed in claim21 or 22, wherein at least one white pigment is present in the baselayer.
 25. The film as claimed in claim 21 or 22, wherein at least oneflame retardant is present in the base layer.
 26. A process forproducing a thermoplastic film as claimed in claim 1, in which acrystallizable thermoplastic is melted in at least one extruder, and theresultant polymer melt corresponding to the composition of the filmlayer, or the resultant polymer melts corresponding to the compositionsof the outer and base layers, are fed to a die or, respectively, to acoextrusion die, and are extruded from the die onto a chill roll, andthe resultant prefilm is then biaxially oriented and heat-set, where thepolymer melt for the base layer or for the outer layer or layers or forthe base layer and the outer layer or layers comprise one or more of aflame retardant a white pigment, and the polymer melt for the outerlayer or layers comprise at least one UV stabilizer.
 27. The process asclaimed in claim 26, wherein the addition of one or more of the flameretardant, the UV stabilizer and the white pigment takes place by way ofmasterbatch technology.
 28. The method of making an interior decoration,a display, a placard, a protective glazing, a shop outfit, a promotionalitem, a laminating medium, a roofing system, an external cladding, aprotective covering, or an illuminated advertising profile or blindwhich comprise converting a film as claimed in claim 1 into an interiordecoration, a display, a placard, a protective glazing, a shop outfit, apromotional item, a laminating medium, a roofing system, an externalcladding, a protective covering, or an illuminated advertising profileor blind.